We previously identified a subset of highly malignant neuroblastoma (NB) tumours with long telomeres which undergo continuous shortening because they lack a telomere maintenance mechanism (TMM), potentially representing a novel therapeutic group. So far, only two TMM-negative NB cancer cell lines have been identified. Here, we searched for additional TMM-negative lines, and also investigated the sensitivity of this cancer subtype to a focussed panel of clinically approved compounds. TMM status was determined using the c-circle assay (CCA), alternative lengthening of telomeres [ALT]-associated promyelocytic leukaemia body (APB) assay, and the quantitative telomere repeat amplification protocol (qTRAP) assay of telomerase activity. Telomere length was monitored over time by terminal restriction fragment (TRF) analysis. Four cell lines were chosen for detailed TMM analysis on the basis of a screen of a panel of 104 NB cell lines that identified them as being potentially TMM-negative. The four candidate cell lines were telomerase-negative by qTRAP and showed low CCA activity and low levels of APBs. However, there was no evidence of significant telomere shortening when the cells were cultured for up to 167 population doublings. We therefore conclude that telomere length is most likely maintained in these four cell lines by ALT activity, albeit in the absence of typical phenotypic hallmarks of ALT. Drug sensitivity was measured in 10 cell lines (two TMM negative, three telomerase-positive, three ALT-positive and two control cell lines with long telomeres) using live cell IncuCyte Zoom proliferation assays. The results showed that TMM influenced drug response and suggest that TMM-negative NB cells have heightened sensitivity to topoisomerase I and topoisomerase II inhibitors. These results will be further validated through ongoing investigations of a larger panel of tumour-derived cell lines that lack hallmarks of a known TMM.